There is some amount of time (window 1) before it comes into contact with the right receptor cell and it binds and starts reproducing.
I don't know how long that takes. If you breathe only breath in a couple of particles, that might take a while. Breath in a lot and it's probably instant.
Once it starts reproducing, it's in the sinuses or throat or eyes. And it reproduces there first, before traveling to other parts. That's window 2. Not sure how long that takes either. Again depends on initial exposure, where it infects, etc.
But it usually takes 5 to 7 days for it to reproduce enough that you start feeling the effects. And probably the effects aren't from the virus but your own response system. But the two are correlated somewhat.
If you catch it in window 1 before it infects, maybe you can prevent an infection. If you catch it in window 2, maybe you can slow it down enough that your immune system ramps up enough to deal with it, and prevent a bad infection.
All speculation, but I think informed speculation.
The body is a hostile environment, and the vast majority of particles are defective. The upshot is it usually takes thousands of particles to become infected. In the case of nCV-2019 it's usually minutes to hours of inhaling air from an infected person producing normal amounts of droplets through breathing. If the other person is speaking or singing or yelling they will produce more droplets.